Rapid latensification of printout material



Oct. 13, 1964 J. H. JAcoBs RAPID LATENSIFICATION oF PRINToUT MATERIAL Filed sept. 14. 1959 HAZ,

'labo ma United States Patent O 3,152,902 RAPTD LATENSIFECATN 0F PRINTOUT MATERIAL .lohn H. Jacobs, Altadena, Calif., assigner, by mesne assignments, to Consolidated Electrodynamics Corporation, Pasadena, Calif., a corporation of California Filed Sept. 14, 1959, Ser. No. 839,618 3 Claims. (Cl. 96-50) The present invention relates to the iield of recording on printout material and, more specifically, relates to the rapid latensification of such material Without fogging.

Materi-als which carry a photosensitive emulsion on one surface, such that an image recorded on the emulsion may be rendered visible by appropriate processing, are well-known. Such materials may have a variety of emulsion compositions. However, the basic constituents of such emulsions are a silver halide compound, usually in -a matrix of gelatin. The silver halide compound is present in the form of crystals, usually triangular or hexagonal in conliguration. The process by which an image is recorded by means of the silver halide crystals is not wellunderstood, even though this process, which is the basic process in photography, has been utilized for many years.

It has been found that rapid l-atensiiication without fogging of printout material can be accomplished by subjecting the exposed printout material emulsion to electromagnetic radiations of wavelengths selected to be within the latensication band of the printout material but Without its range of original recording sensitivity. This statement, brielly, describes the present invention, and the following theoretical discussion is made in an effort to explain the mechanism of operation of the invention as it is presently understood. The recording process consists of a building up of specks of silver atoms about certain loci on the silver halide crystal as a result of exposure of the crystal to electromagnetic radiations. The band of electromagnetic radiation Wave lengths which are operable to initiate such a build-up is hereinafter referred to as the original recording sensitivity of the material.

The following theoretical premises are made in order to provide a basic theory upon which to base an explanation of the invention. A site which acts as the locus of a build-up of silver on the silver halide crystal apparently consists of a silver ion at a discontinuity in the crystal lattice. This ion adsorbs a silver atom to become a latent pre-image speck. The speck is then built up by additional silver atoms to form a latent image speck. The latent pre-image speck has a comparatively short lifetime, Whereas the latent image speck exhibits stable existence.

For a given radiation Wave length Within the original recording sensitivity of the material, the number of such latent image specks which result upon exposure to the radiation is roughly proportional to the product of the intensity and duration of the exposure. This relationship is known as the reciprocity law. However, for a particular material, this process of producing latent image specks has a maximum efficiency at a certain intensity of radiation. At intensity levels either greater or less than this intensity, the process is less eliicient and results in a deviation from the reciprocity laW which is known as reciprocity law failure. At recording exposures which utililize an exposure in the high-intensity reciprocity failure region, apparently a large number of latent sub-image specks, whichV consist of two silver atoms adsorbed to a silver ion, result on the silver halide crystals during the recording exposure, rather than latent image specks.

So long as the silver halide crystals remain in existence as crystals, the image is said to be a latent image. The latent image is developed by the reduction of those silver halide crystals which contain latent image specks to metallic silver (chemical development); or the deposition on those crystals containing latent image specks of silver not directly derived from the silver halide crystal, which deposition is dependent upon the number of latent image specks on the silver halide crystal (physical development). In addition, the recording radiations may themselves actually decompose the silver halide crystal so as to produce a metallic silver deposit at the latent image speck site (photolysis).

Recording materials are well-known which make use of various combinations of chemical and physical development and photolysis in order to make the record itself visible soon after the actual act of recording. Recording radiations in the high-intensity reciprocity failure region are utilized with materials of this type in high speed oscillography. These materals are comparatively insensitive to radiations Within the original recording sensitivity of the materials which are of low intensity, as are found in ambient lighting, for example. The recorded image is itself made visible by the action of material already in the emulsion, which is usually activated by exposure of the material to electromagnetic radiations. These materials do not require the subsequent application of a developing solution to render the image visible. Such recording materials are known as printout materials or printout papers.

Some early efforts relating to the use of printout materials to produce a continuous visible record of inform-ation are illustrated in the following patents:

German Patent No. 872,155 German Patent No. 880,496 U.S. Patent No. 2,580,427

The process by which the image is made visible on printout materials by the exposure of the material to electromagnetic radiations is referred to, hereinafter, as latensiication, although the actual process so designated embraces combinations of chemical and physical development of the latent image by materials already in the emulsion and photolysis of the silver halide crystals containing latent image specks. The Word latensitication, as used hereinafter, is therefore not limited to the build-up of silver atoms at latent pre-image or sub-image specks to form latent image specks on silver halide crystals.

The term access time is used to indicate the time interval between the exposure of a photosensitive material to an electro-magnetic recording radiation and the presentation of a visible record for observation. Conventionally, latensification of printout materials is carried out at normal room lighting intensities. The latensiiication of printout materials by this conventional method has resulted in access times in the range of magnitude of thirty or more seconds for latensilication with satisfactory distinctness of the record.

It is. often desirable and even necessary to record information at printout material transport speeds in the order of magnitude of several inches per second s o as to provide a useful record. in order toi latensify the image recorded at such speeds, continuous exposure of the material to latensifying radiations for ther thirty-second period is still necessary in conventional practice. i-t is readily apparent that the amount of printout material which must be exposed to light over any prolonged period at such speeds is so great as` to have made impractical the use of such speeds heretofore.

Attempts to increase the rate of latensification and thus reduce the access time o-f a printout material by utilizing higher latensifying radiation intensities have heretofore resulted in fogging of the material. the printout material is caused by the exposure of the material to high-intensity radiations within the original recording sensitivity of the material and the resulting for- Patented Oct. 13, ll

Thus,

Fogging of mation of randomly distributed latent image specks Fogging causes a lack of contrast to exist between the background of the printout material and the latent image corresponding to the recorded intelligence. Thus, the rate of latensification of printout materials heretofore could not satisfactorily be increased by subjecting printout materials to latensifying radiations of higher intensity to give an access time of appreciably less than thirty seconds without fogging the record.

According to the present invention, access times of less than one second are achieved by the rapid latensification Without fogging of printout materials by utilizing a selected spectrum of latensifying electromagnetic radiation wave lengths. These latensifying electromagnetic radiation wave lengths differ from and are exclusive of the wave lengths of electromagnetic radiations which correspond to the original recording sensitivity of the printout material.

The invention may be more readily understood by reference to the accompanying drawing in which:

FIGURE 1 is a sec-tional View of an apparatus for the recording and rapid latensification of printout material according to the invention; and

FIGURE 2 is a graphical representation of the printout material sensitivity to electromagnetic radiations.

With reference to FIG. l, a recording oscillograph has 11 has an outer case 12. A galvanometer mirror 13, connected to a galvanometer (not shown), reects light directed thereon from a light source 14. The light source 14 may be, for example, a conventional mercury vapor point source commonly used in recording oscillographs. The light reected from the galvanometer mirror 13 passes through an aperture 15 in an inner dividing Wall 16 of the oscillograph 11. Printout paper 17 contained in a roll 18 passes around a recording roller 19 positioned adjacent the aperture 15 so that the light refiected through the aperture 15 falls upon the printout paper 17. The printout paper 17 then passes around an idler roller 20 and onto a platen 21.

A latensifying radiation source 22 produces radiations which fall upon the printout paper 17 as it passes along the platen 21. After leaving the platen 21, the printout paper 17 is carried between a drive roller 24 and a second idler roller 25. These two rollers 24 and 25 provide the traction by means of which the printout paper 17 is unrolled from the roll 18 and passed along the path just described. Upon passing through the rollers 24 and 25, the latensied printout paper 17 issues from an aperture 27 in the oscillograph outer case 12 and is available for viewing, editing, and, if desired, permanent fixing of the image.

It has been found that various types of printout materials exhibit latensiiication bands of differing widths enoompassing generally contiguous portions of the ultraviolet and visible spectrum. For example, the printout paper of one manufacturer exhibits a latensification band which extends from electromagnetic radiation Wave lengths )of 2500 Angstrom units to 4700 Angstrom units, as is illustrated by solid line 30 and dotted line 31 in FIG. 2. The latensification band of the printout paper of a second manufacturer extends from 2500 Angstrom units to 5700 Angstrom units, as is illustrated by line 30 and dotted line 32 in FIG. 2.

It has been found that such printout materials have a band of original recording sensitivity which falls in a discrete region of the spectrum encompassing both ultraviolet and visible radiations between 3500 and 4300 Angstrom units. Thus, the original recording sensitivity band is narrower than and included Within the latensification band. The exact limits of the band are determined by the particular material. Electromagnetic radiations within this range constitute those radiations Which, when projected upon the printout paper 17 by means of the galvanometer mirror 13 (FIG. l), produce the latent subimage specks. The latent sub-image specks, at which points the latent image specks subsequently form, result from the exposure of the particular portions of the printout material to electromagnetic radiations within the range of the original recording sensitivity of the material in a configuration corresponding to the intelligence to be recorded.

Radiations which are in the general infrared region are beyond the upper limit of the latensification band, that is, the maximum value in Angstrom units of radiations which exhibit the characteristic of rapid latensification, and exhibit a desensitization effect when projected upon latent images recorded on these printout materials prior to latensification. This desensitization effect apparently is a manifestation of the wellknown Herschel effect, and is illustrated by dotted lines 33 and 34 for the papers of the first and second manufacturers referred to above, respectively, and solid line 35 in FIG. 2. In the Herschel effect, a latent image formed by electromagnetic radiations of a certain wave length is destroyed by subjecting the latent image to radiations of an appreciably longer wave length. Although the Herschel effect is not particularly strong in most printout materials, the upper limit of the radiations useful for latensication in accordance with the invention apparently is defined by the radiation wave length at which the effect commences to be manifested. However, because latensication according to the invention is a high intensity process and the Herschel effect is normally a low intensity effect, the upper limit of latensifying radiations according to the invention is not well-defined.

According to the invention, rapid latensiication, with the elimination of fogging, is accomplished by selecting the latensifying electromagnetic radiations so as to fall within the range of the latensitication band of the printout material but outside of the band of the original recording sensitivity of the printout material. For example, in the second printout material described above, that having a latensification [range of from 2500 Angstrom units to 5700 Angstrom units and an original recording sensitivity of from 35 00 Angstrom units to 4300 Angstrom units, the latensifying electromagnetic radiations are selected so as to fall within either or both of the ranges of from 2500 to 3500 Angstrom units and from 4300 to 5700 Angstrom units. Such a latensification spectrum can be achieved by the use of a broad radiation spectrum and selected filters. However, the use of such filters necessitates extremely sharp cut off frequencies adjacent the range of original recording sensitivity. A preferable practice of the invention is to select a latensification source exhibiting bands of electromagnetic radiation which fall Within the above ranges. Any undesirable band of radiation is then filtered out, if necessary, by the use of an appropriate filter.

It is even more preferable practice to utilize a radiation source producing radiations only within the prescribed ranges. In the example given above, a satisfactory radiation source is provided by an Osram Spectal Zinc lamp, with the reservation that a single radiation line at 6362 Angstrom units exists. However, this radiation line has not proved to be so detrimental to the process as to justify its elimination by filtration.

inasmuch as the rapid latensification of printout material is a novel process, data on the various printout materials with regard to the practice of this invention are not available. Therefore, it is necessary, with respect to the various types of printout materials, to experimentally determine the original recording sensitivity range and the latensification range of the material.

The determination of the original recording sensitivity and latensification ranges of a particular printout material is accomplished by first recording intelligence on a strip of the printout material. Latensification is preferably made utilizing a white light source, so as to subject the printout material to radiations having a broad range of wave lengths. The spectrum of the anticipated latensieation range of the printout material is spread out according to wave length by means of a spectrograph. This spectrum is projected upon the strip of the printout material on which the information was recorded.

The latensication band of the printout material is apparent from the strip of printout material so exposed, as corresponding to the wave lengths at which the recorded image has been latensied. The region of original recording sensitivity of the material corresponds to that portion of the strip of printout material which exhibits both latensication of the recorded intelligence and background fogging. In extreme cases, the fogging may obscure the image. In the region of the upper limit of the latensification band, the latensication effect is less pronounced. Due to manifestation of the Herschel effect in this region, latensication of the recorded image may not occur upon subsequent exposure of this portion of the material to radiations Within the latensii'lcation band. Having determined the spectral ranges for latensification without fogging, the lower limit for latensitication radiations, and the upper limit of the latensifcation radiations, i.e., the wave length at which the Herschel effect becomes significant, an appropriate latensication radiation source is selected by comparing radiation spectrums for various of available sources of radiation with the radiation spectrum required for rapid latensication of the printout material according to the invention.

The source chosen for the latensication radiations may emit significant amounts of radiation beyond the upper limit of the latensication band. Whether or not these radiations are such as to degrade the quality of the latensifed image must be determined experimentally for the particular radiation source and printout material. The latensication process usually becomes less efficient in the region of the upper limit of the latensiilcation band. This region may or may not overlap the region in which the Herschel effect normally becomes significant for the particular printout material. Thus, in the practice of the invention, the upper limit of the latensication band is dened by that region beyond which, for the particular printout material and latensication spectrum utilized, additional radiations of longer wave length are not significantly useful to produce latensication of the recorded image. However, the use of a latensifying radiation source emitting, in addition to radiations within the latensication band of the material, such additional radiations of longer wave length, constitutes practice of the invention whether or not such longer wave length radiations actually produce any latensification of the recorded image.

I claim:

1. A recording process for high speed photorecording on an elongated strip of print-out recording paper having a photosensitive silver halide emulsion on one surface thereof, which comprises drawing the recording paper past a point of exposure to a light stimulus to be recorded to form a latent image thereon, which high intensity light stimulus includes radiations in a first portion of the spectrum to which print-out paper is photosensitive under recording conditions drawing the exposed paper past a region of secondary exposure, and

directing on the paper in the region of secondary exposure a second light stimulus substantially free of radiations to which the paper is initially photosensitive and of such high intensity as to rapidly latensify the previously recorded latent image and such that the paper would fog to the serious detriment of the recorded image if radiations to which the paper was initially photosensitive were present.

2. A recording process for high speed photorecording on an elongated strip of print-out recording paper having a photosensitive silver halide emulsion on one surface thereof, which comprises drawing the recording paper past a point of exposure to a high intensity light stimulus to be recorded to form a latent image thereon, which light stimulus includes radiations in a irst portion of the spectrum between about 3500 to about 4300 Angstrom units to which print-out paper is photosensitive under recording conditions,

drawing the exposed paper past a region of secondary exposure, and

directing on the paper in the region of secondary exposure a second light stimulus substantially frree of radiations in that portion of the spectrum between about 3500 to 4300 Angstrom units and of such high intensity as to rapidly latensify the previously recorded latent image and such that the paper would fog to the serious detriment of the recorded image if radiations in the portion of the spectrum between about 3500 to about 4300 Angstrom units were present.

3. A process for latensifying the recorded record on an elongated strip of print-out recording paper having a photosensitive silver halide emulsion on one surface thereof which has been exposed to a high intensity light stimulus to be recorded to form a latent image thereon, which comprises drawing the exposed paper past a region of latensifying exposure, and

directing on the paper in the region of latensifying exposure a light stimulus substantially free of radiations in that portion of the spectrum to which the recording paper is photosensitive under recording conditions and of such high intensity as to rapidly latensify the previously recorded latent image and such that the paper would fog to the serious detriment of the recorded image if radiations in the said portion of the spectrum were present.

References Cited in the file of this patent UNITED STATES PATENTS 1,840,351 Douden Jan. 12,1932 2,026,899 Kipphan Jan. 7, 1936 2,220,882 Bennes Nov. 12, 1940 2,322,082 Wynd June 15, 1943 2,352,914 Rackett July 4, 1944 2,553,841 Andreas May 22, 1951 2,580,427 Heiland Jan. 1, 1952 2,615,778 Butz Oct. 28, 1952 2,710,256 Eckler et al. June 7, 1955 OTHER REFERENCES Baines: The Science of Photography, 1958, Fountain Press, N Y., pp. 166-176.

Dybvig et al.: Photographic Engineering, voll. 5, No. 2, 1954, pp. 127-132.

The Focal Encyclopedia of Photography, vol. 1, 1958, The Focal Press for the Caxton Publishing Co., Ltd., N.Y., pp. 627-628.

John et al.: Photographic Chemistry, 1963, Reinhold Publishing Corp., pp. 104-106.

Beck: Hilfsbelichtung einst und jetzt und deren Theorie, Photographische Industrie, February 16, 1925, pp. 163-164.

Clerc: Photography, Theory and Practice, (2nd Ed), Greenwood and Co., London (1937), pages 330, 346 and 347.

Mori: Hypersensitization by Uniform Pre-Exposure or Post-Exposure, as reported in Monthly Abstract Bulletin, May 1951, page 163. Sheppard: The Optical Sensitizing of Silver Halides by Colloidal Silver, Journal of the Franklin Institute, vol. 210, pp. 587-607. July-December 1930. Note the bibliography at pp. 606 and 607. Especial reliance on page 587, rst paragraph, and page 590, rst complete paragraph. 

1. A RECORDING PROCESS FOR HGH SPEED PHOTORECORDING ON AN ELONGATED STRIP OF PRINT-OUT RECORDIN PAPER HAVING A PHOTOSENSITIVE SILVER HALIDE EMULSION ON ONE SURFACE THEREOF, WHICH COMPRISES DRAWING THE RECORDING PAPER PAST A POINT OF EXPOSURE TO A LIGHT STIMULUS TO BE RECORDED TO FORM A LATENT IMAGE THEREON, WHICH HIGH INTENSITY LIGHT STIMULUS INCLUDES RADIATIONS IN A FIRST PORTION OF THE SPECTRUM TO WHICH PRINT-OUT PAPER IS PHOTOSENSITIVE UNDER RECORDING CONDITIONS DRAWING THE EXPOSED PAPER PAST A REGION OF SECONDARY EXPOSURE, AND DIRECTING ON THE PAPER IN THE REGION OF SECONDARY EXPOSURE A SECOND LIGHT STIMULUS SUBSTANTIALLY FREE OF RADIATIONS TO WHICH THE PAPER IS INITIALLY PHOTOSENSITIVE AND OF SUCH HIGH INTENSITY AS TO RAPIDLY LATENSIFY THE PREVIOUSLY RECORDED LATENT IMAGE AND SUCH THAT THE PAPER WOULD FOG TO THE SERIOUS DETRIMENT OF THE RECORDED IMAGE IF RADIATIONS TO WHICH THE PAPER WAS INITIALLY PHOTOSENSITIVE WERE PRESENT. 